snip~SAN FRANCISCO — Downloading a gun design to your computer, building it with a three-dimensional printer that uses plastics and other materials, and firing it minutes later. No background checks, no questions asked.

Sound far-fetched? It's not. And that is disquieting for gun control advocates.

Rep. Steven Israel, D-NY, said the prospect of such guns becoming reality is reason enough for the renewal of the Undetectable Firearms Act, which makes it illegal to build guns that can't be detected by X-ray or metallic scanners. That law expires at the end of 2013.

At least one group, Defense Distributed, is claiming to have created downloadable weapon parts that can be built using the increasingly popular new-generation of printer that can create 3-D objects with moving parts.

University of Texas law student Cody Wilson, 24-year-old "Wiki Weapons" project leader for Defense Distributed, says the group last month test fired a semiautomatic AR-15 rifle — one of the weapon-types used in the Connecticut school massacre. Video posted by the group on YouTube indicates the gun was built with some key parts created on a 3-D printer and fired six times before it broke.